Added three new built-in resource types: container-instance,
devcontainer-instance, and devcontainer-file. The devcontainer-instance
type inherits from container-instance per ADR-042 and is auto-discovered
when git-checkout or fs-directory resources contain .devcontainer/
directories per ADR-043.
Implementation includes:
- DevcontainerHandler extending BaseResourceHandler with snapshot strategy
- Auto-discovery module scanning .devcontainer/devcontainer.json and
root .devcontainer.json with JSON validation
- CLI support for devcontainer-instance and container-instance via
agents resource add with --path and --image flags
- Behave feature with 22 scenarios covering manual registration,
auto-discovery, invalid JSON handling, and protocol conformance
- Robot integration tests with 10 test cases for CLI round-trip and
DAG hierarchy validation
- ASV benchmarks measuring discovery throughput with varying subdirectory
counts, handler resolver cache performance, and result construction
- Reference documentation at docs/reference/devcontainer_resources.md
ISSUES CLOSED: #511
